There are 65 abilities you get from one playthrough on any difficulty. Once all 65 have been purchased a 66 ability will show up, Never Dismember. To make this a little faster you can attach the Extra XP, Extra XP+ & Extra XP++ abilities. Or use the Panda Bear XP boost.
- 65 abilities require 3 000 000 XP
- 66 abilities require 13 000 000 XP
- Never Dismember cost 10 000 000 XP
Note: Not until you buy the Never Dismemberment ability will the achievement unlock
nikolai429 shared the Panda Bear XP boost/farm HERE!